Edited README.md to mention support for sub-commands

Author: tleonhardt

README.md

@@ -29,11 +29,11 @@ Main Features
 - Multi-line, case-insensitive, and abbreviated commands
 - Special-character command shortcuts (beyond cmd's `@` and `!`)
 - Settable environment parameters
-- Parsing commands with arguments using `argparse`
+- Parsing commands with arguments using `argparse`, including support for sub-commands
 - Unicode character support (*Python 3 only*)
 - Good tab-completion of commands, file system paths, and shell commands
 - Python 2.7 and 3.4+ support
-- Linux, macOS and Windows support
+- Windows, macOS, and Linux support
 - Trivial to provide built-in help for all commands
 - Built-in regression testing framework for your applications (transcript-based testing)